it is because the thermostat opens and the level can drop a
little
.
My 2000 Chevy Suburban (Vortec 5.3 engine) occasionally
flashes a
trouble alarm that the coolant level is low. By
occasionally, I mean
maybe a total of 5 times during the last 6 months. It occurs
after an
hour or more of driving
and it doesn't seem to be affected by ambient temp. or
engine temp.
Engine temp always runs normal. Last week it came on for the
first time
in several months. When the
alarm comes on. I have verified that the level is low. I
looked at my
owner's manual and to my surprise, it suggests that the
level should
fall slightly when the car reaches operating temp.
Yesterday, I
verified that this does occur although it fell only about a
half inch
or so. Why should the level fall? The only answer I can
think of is
that the hoses expand when they are hot and pressurized. I
believed
that explanation more when I saw the level go back to the
COLD normal
when I cracked the cap and let the pressure subside. I
have never added coolant in the 2+ years that I have owned
it. This
past June I made a 4000 mile trip and the alarm never came
on.
Similarly, in September I was a hurricane Rita evacuee stuck
in endless

traffic jams and the alarm never came on.
So, my questions are:
1. What could cause the level to occasionally and
unpredictably become
extra low when the engine warms up?
2. Why does the level fall at all with increasing engine
temperature?

I will go ahead and add coolant so that the cold level is
about an inch
above the COLD mark. Maybe that will cure the problem for
ever.

If you'd like to email me directly, reverse the 1st 4
letters of my
address.